An approach to the systematic neglect of the small-in-value electron repulsion integrals which is used in a number of approximate self-consistent field molecular orbital schemes. It means that all the products of atomic orbitals ${\text{χ}}_{\text{μ}}{\text{χ}}_{\text{ν}}$ are set to zero and the overlap integral ${\text{S}}_{\text{μ}\text{ν}}={\text{δ}}_{\text{μ}\text{ν}}$ (where ${\text{δ}}_{\text{μ}\text{ν}}$ is the Kronecker delta). The ZDO approximation greatly simplifies the computation of wavefunctions by eliminating many of two-electron integrals. At the ZDO approximation all three- and four-centered integrals vanish.